K10D Focusing, Part III

Or, "Curiouser and Curiouser".

 

The Pentax rep who answered the phone swore it was merely a "calibration" issue related to the lens(es)

I was using, despite my repeated mentions that I was focusing manually so therefore it couldn't be a

simple issue of a misconfigured AF system. I suppose I could have pressed the issue and escalated it to

a technician, but I decided to wait another day and gather more data to use as verbal ammunition in

tomorrow's struggle to get to talk to a real camera technician.

 

I ended up putting almost all my lenses on the K10D, and focusing on the same test scene (a medicine

box with some fine print on it at the midpoint of a sloping ruler), and exposing a lot of test shots. Darned if there isn't a difference from lens to lens after all.

 

By far the worst back-focuser is the brand-new DA* 16-50mm zoom. It's several times worse than any

other lens in this regard, back-focusing by several inches in the test scene.

 

Most of the other lenses back-focus by 1 cm or so. But my cheapo manual focus 35-80 kit zoom from

years back pretty much focuses spot-on! And if my new Sigma 70mm macro lens isn't spot-on, it's

very close to being so.

 

And remember, this is all when using manual focus (though I doubt AF would make much difference, as

in my experience it agrees with my eyes). So it can't be a simple matter of a misconfigured AF sensor.

 

The only thing I can think of is that for some reason the camera is using the shake-reduction mount

that holds the CCD to move it in and out a little depending on what lens is mounted. I do have shake

reduction turned off, of course, but that doesn't _necessarily_ mean the body has locked the sensor

into one fixed, immobile position until the SR switch is turned on.

 

One would expect it to, of course, but a sensor whose distance from the lens mount changes depending

on what lens is mounted is the only thing _I_ can think of that can explain this odd behavior I'm seeing.

 

It all begs a bevy of other questions, which I'm going to ask a technician later (hopefully tomorrow). For

openers, I want to be sure that fixing the focus on my DA* lens won't make it worse for my other

lenses. Then there's the issue that two of my lenses aren't made by Pentax and how to get them to

work properly.

It would be interesting if you could get ahold of a K100D, and try the same lenses on it to see the results by comparison.

OK, now you've got me wondering about my camera (a k100 not k10). For the life of me I am unable to focus my 50mm M 1.4 lens wide open (manually of course). Things that I *think* look tack sharp in the viewfinder are inevitably out of focus in the photo. I can take 5 shots of the same thing in a row, refocussing each time, and get 5 shots out of focus. I've been assuming that it is just because I don't have a focussing screen, but the fact that others don't seem to have the same problem and your comments about back-focus are beginning to make me think that either this lens or my camera body have an issue.

 

Hmmmmmm.

I will retest my lens an try and work out where the focus point actually ends up. Presumably if it is always in front of or behind the point I intended then something is screwy. If it varies all over the place then it is just my eyes =-/

Ashley- I have the K100D and I think the same lens too, Asahi SMC Pentax-M 50mm/1.4. Nice lens, but I am having the same problem you described. Actually seem to have the same problem with other lenses too- which are all manual focus.

 

I haven't been sure enough to rule out my bad vision, that Ive adjusted the viewfinder diopter correctly, or even in some shots that the lack of sharpness when I'm zoomed in on my computer is perhaps the way the stabilization is dealing with camera shake. Then of course the dreaded fear of something being wrong with the camera or the lens.

 

All I know is that most of my shots look in focus in the viewfinder, to my eye, but when I open the images in editing software my focus seems off on too many for my liking. I'll have to play with it some more to rule out other variables.

 

And I'm looking to the K10D as my next move up, so I'm interested in this thread.

Dave,

 

I don't think the SR system even allows movement of the sensor toward or away from the lens mount. I think it only goes up/down, left/right, and rotationally--not forward and back.

 

You said most of your lenses back-focus by about an inch... how many lenses did you test? It seems logical that your DA* might have issues, considering the unfortunate amount of problems Pentax has been having with the 16-50. It also doesn't seem unreasonable that your old MF lens and Sigma lens might be front focusing, considering the older lens might have gotten jostled around in it's long life and Sigma (again, unfortunately) frequently has QC issues.

 

If I had to guess, I'd say your prism was mis-aligned. That would cause your AF to read a focus lock while the image still wasn't at the exact plane of focus in relation to your image sensor. It would also give you a false view of what is in focus while manually focusing your lenses.

 

 

How many tests did you do with each lens? I ask only because I just had a thought that perhaps your prism isn't quite as secure as it needs to be, and maybe it's changing position on you. However, if each lens tests the same way over and over again, then this probably isn't the case.

 

good luck figuring this out! and i hope you have a backup body to play with in the meantime!

"If I had to guess, I'd say your prism was mis-aligned."

 

This makes no sense to me. The problem affects both autofocus and the image in the finder. If the K10D' SAFOX VIII autofocus is anything like earlier versions of SAFOX and other phase-matching AF systems, the optical finder plays no role in it. The AF is based on second CCD sensor below the reflex mirror (which is only partially silvered in the center in order to let some light into the AF sensor).

 

I suppose by some accident the AF sensor and the focusing screen could both be misaligned by the same amount, but: (a) the odds of that are pretty slim, and (b) it wouldn't explain how different lenses focus differently (if it was a simple fixed misalignment, all lenses would backfocus).

Oh, also, I can't see how a loose prism would cause focusing errors. In an SLR, manual focusing is based on an image projected on a ground-glass screen that precedes the prism in the light path. A loose or misaligned prism could cause composition errors, but not focusing ones. (The latter could, however, be caused by a misaligned ground-glass screen or reflex mirror.)

 

This also means that the diopter adjustment can't be at fault, since it is possible for me to get the image in the finder to be sharp. A misconfigured diopter adjustment can only take a sharp image on the ground glass and make it blurry. It can't do the reverse.

"The AF is based on second CCD sensor below the reflex mirror (which is only partially silvered in the center in order to let some light into the AF sensor)."

 

Well, there goes my theory! ;)

Pentax USA wasn't particularly helpful. They refused to let me speak to a repair technician or to relay my questions to one. The phone rep was obviously working from a standard script related to a problem that affected autofocus only.

 

I live in Portland, so I called Advance Camera in neighboring Beaverton, whom I had heard was an official Pentax factory service depot authorized to perform repairs under factory warranty. (They are.)

 

Within a minute I was speaking to a repair technician. He said my combination of symptoms was very strange and that he couldn't remember seeing another K10D with such symptoms. He wanted to see the camera himself and personally examine it.

 

So I'll probably be making a trip to Beaverton in the next few days to drop the camera off and let him do just that.

Darren, it sounds to me like your diopter isn't adjusted correctly. I had the same issue as you, and ended up having to buy a diopter adjuster because the range of the diopter wasn't enough for me. It goes up to +2.5, but I need +3.5!

 

The way you can check this is by using autofocus and checking what you see in the viewfinder and on the actual file. If AF gets your shots in focus, but your eye doesn't, then you need to adjust the diopter.

 

David, good luck to you! I think you will be better off handing the camera off to that technician close to home than sending it off to Pentax for 6 weeks.

I just noticed the post tonight and had that "ah" feeling. Sunday night, I was trying to take some pics of seedlings for POW and was using my Pentax A 50mm Macro F/2.8. I took about six shots which where in focus when I looked through the view finder but we really unfocused when I opened them up in PS. I wrote it off to my inexperience at the time as I was shooting @ 125th 400ASA and thought maybe a little bit of camera shake came into play. I had SR turned off. As this lens is fully manual I am unable to take Mis's advice. Any other ideas I can try to check it out?

My apologies if I'm getting off the thread topic too far... Miserere- thanks for your friendly comments. I'll have to play with it a bit more but at this time i do not have any AF lenses, just four different manual ones from my old Program Plus film days. And no plans to buy any more lenses in the immediate future. I wasn't sure exactly how the diopter works - I thought i just look through the viewfinder and slide the adjuster around until things look clear. but I guess with a manual focus lens that's like trying to hit a moving target.

David- at any rate, I'm looking forward to hear what the local tech has to say. Still dreaming of upgrading to a K10D or K20D some day.

Oh, and Michael- just read your post, and yeah same deal here. Miserere loves company? lol, either bad spelling or bad humor or both

The matte focusing screens on most DSLR are apparently not like the ground glass of old.

They have an effective aperture of around f/4 which means that if you are using a faster

aperture, what you see as in focus might not be what the sensor sees. (Google this)

 

When using something like the M50 1.4 wide open try focusing from both close to infinity

and then from infinity to close. I find that if I approach the focus point from the infinity

side, I get much better results.

 

David's problem is something else though -- I too would love to hear what the Pentax

tech says.

Tuyen- thanks for that, very enlightening and somewhat relieving to know that the problem is not likely an equipment defect or my eyes...

This thread is a week or so old & I'm a new member (so I'll try searching for an updated

one) but I wanted to add that have found this focusing issue to be prevalent with my

experiences using the K10d. I happen to otherwise quite like my Pentax system, but have

had to learn to adjust my focus to compensate for the bad backfocus I experience with my

broad assortment of Pentax lenses - which include the 3 main limited primes (33, 43, 77),

an old SMC-A f/1.4 50mm, SMC 28mm, SMC 135 and the DA* 16-50. I also have a few

3rd party lenses that don't seem to exhibit the problem as much but it might be because

they're not as fast as as my Pentax ones & the wider DOF might therefore mask the issue

somewhat.

 

Like I said, I've learned that in critical focus situations (where DOF is razor thin) that I

adjust my focus where it looks correct in the viewfinder & then pull it forward a bit -

making my desired focus point a tad blurry - in order to actually hit it correctly in the final

image (I use manual focus & full manual settings 90% of the time). For a very long period,

I blamed myself for bad shots until I was able to verify that it wasn't me, but something

wrong with the camera.

 

If it wasn't for my love of Pentax glass & my obviously sizable investment in it, I probably

would've jumped ship at that point. Though it is worth noting that I've discovered other

manufacturers have had this problem with their DSLRs as well. After doing a bit of

research online, I'm not convinced that sending my camera in would resolve the issue

either - not that I could afford to wait the ridiculously long time to get my camera back

anyway (I do work professionally as a photographer). I'd rather use my 'adjusted focus'

method & take advantage of the higher megapixels & greater imaging of my K10, than use

my older Pentax DSLR (or film SLRs!).

 

Anyway, I wanted to add my voice to this short thread for others who might be searching

for answers to this annoying problem. If anyone actually has found a satisfactory solution

to this problem, please share it with me!

Sorry, above should read (31mm, 43mm, 77mm) - was typing too fast :)

Hello, everybody,

After reading this thread I also decided to write about my experience with the K10D backfocusing. Currently I have three Pentax lenses - my older FA 50/2.8 Macro (sold all older zooms). This one seems to work fine with no focusing problems. My DA 16-45/4 (which I bought together with my first DSLR - istDL) backfocuses badly. It doesn't matter if I focus in AF or manual, results are consistently the same - strong backfocusing, although the picture looks sharp in the viewfinder. I also have learned for now to frontfocus manually a little (just by guesing how much) so that the resultant picture is sharp. Odly, the DA 18-55 that I bought together with the K10D, seams to have no backfocusing problems. I wish it were opposite, because I like the 16-45/4 more.

I hope Pentax will release a firmware update that substantially improves the focusing performance (best would be an option to adjust AF in menu, as it is possible in K20D, at AT LEAST FOR A FEW different lenses).

In film era I had no such problems with Pentax, and I enjoyed Pentax cameras (my MZ-5n still with me, collecting dust now). Pentax also used to provide good service with my film equipment. I hope they will remain cooperative in the digital era and do something about the K10D focusing problem. I have no doubt they know about it. For now, the most frustrating thing is their silence. I think they should be frank and say, if they are working on it, or if it is at all possible to do anything about it. This way they would at least show their cooperative attitude.

Hello,

I'll chime in as well, and report a solution that seems to have corrected most of my

trouble.

 

I've a K10D body, and am just beginning my foray into pentax glass after having

swapped from another well known manufacturer. I noticed the focusing issues right

after I picked up my DA* 16-50mm, and at first just attributed it to the well known

back focusing issues noted for that lens. However, when I put on my Sigma 18-

50mm F2.8 EX (wow! sharp!!) I found that it was now showing almost exactly the

same range of backfocusing issues as the DA* 16-50mm.

 

What??? The sigma was fine before hand (and I've saved images to back that up),

but after having the DA* 16-50mm on the camera for all of a half hour, the sigma

started to exhibit the same problem. At this point I was sure it was something to do

with the body. Maybe the body reads the particular focal length of the lens and

adjusts its memory table to alter the length of the primary light path. The 16-50mm

might have had some additional information to convey which updated the memory

table in a negative manner for that focal length range. Hmm. What to do.

 

I took a round of test shots with a focusing test chart at 45 degrees both right side

up and upside down, as well as a linear plane of objects at varying scalar distances

(percentage wise), and confirmed the backfocusing is similar with both the 16-50mm

DA*, as well as the 18-50mm Sigma. I then tried the other glass I own, a 50mm FA

1.4, and a DA 16-45mm. In the case of the FA 1.4, focus was perfect (well the

argument could be made that perfect focus is 1/3 infront, 2/3 behind but for the sake

of this argument consider 1/2 in front, 1/2 behind to be perfect). The DA 16-45mm

showed the same backfocusing problems.

 

At anywhere from 16- ~28mm, all three wide zooms showed similar back focus

(thought the 16-50mm DA* was the worst) while at 50mm or equivalent they all

appeared to be focusing properly. The 50mm FA 1.4 was spot on at 50mm.

 

After browsing the net looking for a solution, I found the 1.1 firmware with the hidden

debug mode. I modified the header with the 1.3 header (as already I updated to 1.3

firmware) and uploaded to the camera.

 

After playing around with the focusing system, I found that if I adjusted for one lens,

(and in my case, this in practice adjusts for the focal length not just a specific lens,

ie: adjusting for the 16-50 solves the 18-50 etc.) would often put another out,

specifically that there seems to be only one universal setting for front / back focus.

This setting I think is different for different focal lengths, or at least should be, as all

the lenses I've tried show the same problem. It may be possible (and I'll have to do

some more research to understand the math involved with calculating the distance

to the sensor for focusing) that the sensor is calibrated properly for 50mm, but is out

at the wide end. I would imagine that the wider lenses would show even worse

backfocusing (tok 11-16mm anyone?) on the wide end.

 

Could this be a result of a faulty memory table describing focal length adjustments?

I don't really have the skinny on how this works, so don't take this too seriously.

 

Regardless, I continued testing and found something interesting. After adjusting

back to zero with my 50mm FA 1.4, turning the camera off, then swapping to the 16-

50mm DA*, I found that adding +80 to fix the back focus, turning off the camera,

and swapping back to the 50mm FA 1.4, the camera seems to have remembered

that the 50mm was good at zero (but that is not indicated in the menu... it still says

+80.

 

Let me repeat this more succinctly, the 50mm was now spot on at +80 as indicated

in the menu... whereas before it was spot on at zero. At this point I was confused

as to how this would occur, unless the memory table somehow retained info from

the last lens, for a particular focal length. Ok, that was good, I confirmed it with a

few shots, and then went to bed.

 

The next day I started to do some more test shots, but was discouraged to find that

the camera had reverted to the original settings, of adjusting for one, outadjusts

another.

 

I did some more reading on the net about manually adjusting via screws on the

sensor the distance from the mount. Not prepared to do that until I understood more

concretely the math, I decided to continue to catalogue my issues.

 

Long story short, the solution I found goes as follows (though retaining this in

memory seems to be somewhat difficult to achieve, there may be some kind of write

procedure required or it loses the info after a certain amount of power off time.

 

1.start with the least problematic backfocusing lens (or alternatively the most front

focusing of your collection (up to four can be done with this method) and arrange

them in order of increasing back focus. This for me meant: 50mm 1.4, 16-45mm,

18-50mm, 16-50mm.

 

2.with the most front focusing (in my case the 50mm was perfect at zero) go to the

capture setting above the focus setting, and on the first line set the value to 1.

 

3.Calibrate the lens via the back/front focusing adjustment.

 

4.verify focus. Turn off camera. Swap lens to next in series (16-45 in my case)

 

5.Go to the menu as in 2. and increase the value +1.

 

6.Repeat steps 2-5 for each lens up to a maximum of 4.

 

When you are done, exiting debug mode and swapping lenses should produce

correct focusing for each lens. Whether altering the value in the capture menu

'actually' does anything, I'm not 100% on, as this procedure seems to work without

changing this value. However, it has shown improvement on the amount of time the

camera remembers the settings. (I will do a more concrete analysis of these

parameters when I borrow my partners k10d)

 

Anyhow, I hope that helps some of you. If this is far too scattered, I can write

something a little easier to read.

Ok, I've been able to get ahold of another K10d, and it turns out that all of my problems

have now disappeared. No more focus issues with any lens, at any focal length. This

is interesting. I think I may send in this k10 and see what they say.

 

I'm going to compare the exif data to see if this other k10 is significantly different than

the old one.

Hi, everyone again. I called today the official dealers of Pentax here in Lithuania. The woman I talked to was very cooperative and explained that it is best to send the camera for a check-up to them. But from what she said I somehow felt that they are not very enthusiastic about going in for calibration. Well, I decided to try the method advertised here on the Internet and installed first the hacked version 1.10 and then the original Pentax version 1.10 over it. OH, BOY! I didn't have to start doing anything with service menus or anything. All my backfocusing problems are GONE just by installing v1.10!!! Have no idea why or how. But it is what it is. This makes me think that the backfocusing/frontfocusing problems are somehow related to a firmware bug or something. I STILL hope Pentax will be introducing a firmware update correcting the backfocusing issue. (Well secretly I am still nurturing the hope that Pentax will add AF adjustment in menus at least for two or three lenses in a future firmware update. Even this would be extremely helpful.)

Hello. Last time I wrote I was a bit in a rush with my conclusions about v1.10 solving the problem. I had to adjust the focus +100. Now it is really spot on.

I have to say that this saved me. I kept taking photos that just didn't seem tack sharp. I played with the focusing hack a while back but reset it as it seemed to complicated. I then went and shot some with a D1x that I had lying around and those pictures, photo for photo were way sharper which ruled out body sway and my failing eyesight. So today, I got the hack, took a picture of a box that was 2 feet away with writing on it, and what do you know +100 made the photo tack sharp. 120 was too much so was 220.

<p>I know this is a dead thread but i am desperate!!! I am a professional photographer and suddenly my K10 is backfocusing. I have looked for the 'hacked' 1.10 filmware update, but the only thing I find is the 1.30 on the Pentax.ca website. I have several shoots lined up that I will have to cancel if I don't solve this. Any direction would be helpful - where do i find the filmware???<br>

I appreciate all the responses on this post. I have lost much sleep over this. At first I thought it was me, but started realizing it wasn't. wish I haven't invested so much in Pentax...</p>